1. Field of the Invention
This invention is in the field of spacecraft docking systems for nano and micro spacecraft, and in particular permits final precision docking maneuvers to be accomplished in a non-precision manner.
2. Description of the Prior Art
To accomplish precision docking of spacecraft in a micro gravity environment involves the application of highly sophisticated navigation and docking processes. In a satellite servicing mission, a nano (under 10 kg) or a micro (under 100 kg) satellite autonomously docks with a larger satellite and mates with an external electrical/mechanical connector to provide a replacement or upgraded component. Traditional docking mechanisms are small latching devices that require the nano-/micro-satellite to precisely locate and engage the mechanism on the target satellite, placing a tremendous burden on the guidance, navigation, and homing functions of the nano-/micro-satellite. An alternative approach is to provide a large docking area on the target or "Receiver" spacecraft (RSC) to which the "Servicer" spacecraft (SSC) can attach, thus minimizing the guidance requirements for the SSC. This large docking patch or its mate is active, so that it can manipulate and reposition the SSC to the exact location required to engage the electrical/mechanical/fluid connectors to effect the service/replacement/upgrade function.
Several satellite applications of micro-miniature active attachment mechanisms are envisioned for future systems. In a satellite servicing mission, the nano-/micro-satellite might have robotic capabilities and will require attachments which allow it to move about on the host satellite. These attachments (on its feet, for example) must allow attachment, restraint during robot locomotion, and detachment. One approach is evocative of a caterpillar, in which the robot's feet always maintain positive attachment, but are comprised of many active elements that propel the robot.
In some surveillance missions, large deployable structures (such as antennas) are required, and once deployed their shape precisely achieved and maintained. A deployable antenna could consist of segments (like the petals of a flower) which unfurl and attach along their edges to form a dish-like shape. If the edge attachments were active, they could allow small adjustments of the captured position of the mating edges and provide a more accurate deployed shape.
"Smart" attachments are devices that allow two parts to attach and detach, but also effect the relative motion of the two parts (either automatically or on command) while maintaining attachment. It is envisioned that these devices might consist of thousands of miniature attachments (hooks, for example) which are active using smart materials or micro-actuators.
This particular invention focuses on the autonomous precision docking of spacecraft using a non-precision approach, thereby alleviating the requirement for complex and costly satellite navigation and control systems. This invention, however, does not relieve the two spacecraft planning to dock of the requirement to employ sophisticated navigation system to rendezvous locally (&lt;1 meter) via orbital maneuvers. The invention requires that the two spacecraft can be maneuvered in such a manner that the SSC transfer surface contacts the RSC "Smart Docking Surface" (SmDS) in a soft non-impact manner and with a relatively small angular misalignment to the normal of the "smart" surface. The benefit of this invention comes primarily from the relaxation of the Y, Z and Roll coordinate degrees of freedom precision maneuver requirements of the two docking spacecraft. The coordinates are defined in FIG. 1
Relaxation of X, Y and .phi. degrees-of-freedom precision docking requirements leads to a simplified and more robust spacecraft docking control system. This invention creates a new and novel way to dramatically decrease the complexity of the docking processes which enhances the overall spacecraft system design by allowing for less overall spacecraft resources (power, propulsion fuel, computational load) to be allocated for docking events.
Applications for "Servicer" nano and micro satellites include: providing satellite electronics system upgrades and repairs of DoD space assets; replenishment of cryogenics cooling fluids for IR based sensors and/or cryo-electronics satellite subsystems; replenishment of chemical reactants fuels for space based laser weapon systems; and attachment of de-orbit systems to satellites that cannot de-orbit themselves.